1. Field of the Invention
This invention relates to interconnected locks. Interconnected locks are locks in which the outside of the door appears to have two separate conventional locks comprising a latchbolt lock mechanism on the bottom and a deadbolt lock mechanism on the top. On the inside of the door, however, the latchbolt and deadbolt are interconnected so that rotating the inner handle automatically retracts the deadbolt as the latchbolt is retracted.
2. Description of Related Art
From the locked outer side, a door fitted with an interconnected lock appears to have two separate conventional locks. Typically the upper lock appears to be a conventional deadbolt operated by a key to drive a deadbolt and the lower lock appears to be a standard cylindrical or tubular lock that drives a latchbolt. On the inside however, the two locks are interconnected.
A principal advantage of interconnected locks is that they simplify exiting a locked area. With separately installed deadbolt and latchbolt locks, exiting a locked area requires two motions—rotating a thumb turnpiece to retract the deadbolt and rotating the inner handle to retract the latchbolt. To exit through an interconnected lock requires only a single motion. Rotating the inner handle of the interconnected lock simultaneously retracts the deadbolt and the latchbolt.
The convenience provided by the interconnection described above, however, is a security disadvantage for conventional prior art interconnected locks. If a vandal is able to break off or remove the outer handle it may be possible to gain access from outside the locked area through the failed latchbolt lock to the inside spindle or other latchbolt lock components turned by the inner handle. In such a case, the interconnection of a prior art interconnected lock between the latchbolt lock components and the deadbolt lock will allow the vandal to retract the deadbolt as well as the latchbolt by manipulating the components of the interconnected lock on the inner side of the door. When the deadbolt and latchbolt are separately installed, failure of the latchbolt lock mechanism does not affect the security of the deadbolt lock mechanism.
Because latchbolt locks, such as cylindrical locks and tubular locks, are generally less resistant to attack than deadbolt locks, the overall security of prior art interconnected locks is less than for an installation using a completely separate and independent deadbolt and latchbolt lock. There is a need for an interconnected lock design where the deadbolt and latchbolt lock mechanisms interact to provide the advantages of an interconnected lock, yet which is as secure as separately installed and independently operated deadbolt and latchbolt lock mechanisms.
Because of the ease with which a locked area may be exited, interconnected locks are often installed for use by the elderly or infirm. The speed of operation and simplicity of use of the interconnected lock is particularly valuable in an emergency, such as a fire. The benefits may be greatest when the occupant of the locked room is elderly and/or has reduced mental capabilities, as they may not remember to rotate the thumb turnpiece of a separately installed deadbolt before attempting to exit via the locked door.
However, these advantages for the elderly and mentally disabled are offset by the current design of interconnected locks for those who are physically disabled, weak, injured or infirm. Conventional interconnected locks simultaneously retract the latchbolt and the deadbolt as the inner handle is turned. The simultaneous operation of the latchbolt and deadbolt mechanisms requires more torque than operating these elements separately. The elderly and infirm may not be able to easily produce the increased torque required, making the interconnected lock more difficult to operate by those for whom the lock offers some of the greatest advantages.
The use of lever handles to provide more handle torque, as used in public buildings to improve access by the disabled, exacerbates the security disadvantage described above because a vandal can use a lever handle to produce more torque and break the latchbolt lock portion of an interconnected lock. Accordingly, there is a need for an interconnected lock that does not require more torque to operate than the torque required to separately operate a conventional deadbolt or a conventional cylindrical lock.
Another disadvantage of conventional interconnected locks is that they simplify the process of exiting a locked area, but not the process of locking the door. The deadbolt portion of the interconnected lock must still be separately locked by rotating the thumb turnpiece on the inside of the door after the door is closed. Often, this is not done. It would be desirable for an improved interconnected lock design to allow the deadbolt to be extended as easily as it is retracted.